This invention relates to an apparatus and method for applying a resin coating or patch to threaded fasteners. More particularly, the invention relates to an apparatus and method for applying a resin coating or patch to different portions of the fastener, such as its external and internal threads. The invention also relates to a self-locking fastener having both external and internal threads with a resin coating thereon.
This invention is particularly suited for applying a resin coating or patch to threaded inserts, which are fasteners that have both external and internal threads. Threaded inserts are typically installed into a receiving member where its external threads engage the receiving member. A separate externally threaded fastener may be then, in turn, installed and engaged with the threaded fastener's internal threads.
As with other fasteners, certain applications require that the threaded insert be self-locking, and some applications require the self-locking feature on both the external and internal threads of the insert. This has been previously achieved by a technique in which a vertical or horizontal bore is first made in the threaded insert to receive a pellet or strip of resilient plastic. While this technique is effective, it unduly increases the threaded insert's cost due to the additional machining step required.
Various methods and apparatus are also disclosed in the prior art for economically applying resin locking patches or coatings to either the external or internal threads of fasteners. For example, U.S. Pat. Nos. 3,579,684 and 3,858,262 are directed to techniques in which a fastener is heated and heat fusible powdered resin is then sprayed on the external or internal threads. The resin then adheres to the heated threads forming a coating or patch. These methods, however, do not address the application of a patch or coating to both the external and internal threads of a fastener.
It would, therefore, be advantageous to provide an apparatus and method which applies a resin coating or patch to different portions of a threaded fastener, such as both the external and internal threads of a fastener. It would also be advantageous to provide an apparatus which reduces the manufacturing costs of producing a threaded insert which has a reusable self-locking resin coating or patch on both its external and internal threads. Moreover, it would be advantageous to provide a self-locking fastener having both external and internal threads with an applied locking patch of resilient resin material.